R help - Dec 2011 - data frame and cumulative sum

Hello,

I have a data frame that looks like this (containing interarrival times):
> str(df)
'data.frame':	18233 obs. of  1 variable:
 $ Interarrival: int  135 806 117 4 14 1 9 104 169 0 ...
> head(df)
  Interarrival
1          135
2          806
3          117
4            4
5           14
6            1
> 
This corresponds to the time differences (in ms) of a poisson arrival process
where Interarrival{i+1} = time_{i+1} - time_{i}

I want to get the Time bin (in minutes) of every interarrival basically
something like:

1) df$Time <- sum(of all df$Interarrival up to "this rownum") #
cumulative sum
 
2) df$Time <- floor(df$Time / 60000) + 1

then I should get the first minute of Interarrival having 1 and so forth. The
problem is I have no idea how to accomplish 1) in R.

Can anyone advice? 

Thanks in advance,
Best regards,
Giovanni

??"cumulative sum" would almost certainly lead you to cumsum with only
a modicum of effort

Michael

On Wed, Dec 7, 2011 at 5:13 PM, Giovanni Azua <bravegag at gmail.com>
wrote:
> Hello,
>
> I have a data frame that looks like this (containing interarrival times):
>
>> str(df)
> 'data.frame': ? 18233 obs. of ?1 variable:
> ?$ Interarrival: int ?135 806 117 4 14 1 9 104 169 0 ...
>> head(df)
> ?Interarrival
> 1 ? ? ? ? ?135
> 2 ? ? ? ? ?806
> 3 ? ? ? ? ?117
> 4 ? ? ? ? ? ?4
> 5 ? ? ? ? ? 14
> 6 ? ? ? ? ? ?1
>>
>
> This corresponds to the time differences (in ms) of a poisson arrival
process where Interarrival{i+1} = time_{i+1} - time_{i}
>
> I want to get the Time bin (in minutes) of every interarrival basically
something like:
>
> 1) df$Time <- sum(of all df$Interarrival up to "this rownum")
# cumulative sum
>
> 2) df$Time <- floor(df$Time / 60000) + 1
>
> then I should get the first minute of Interarrival having 1 and so forth.
The problem is I have no idea how to accomplish 1) in R.
>
> Can anyone advice?
>
> Thanks in advance,
> Best regards,
> Giovanni
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